Recently a number of proposals have been made to make use of RFID (radiofrequency ID) tags to track mail in postal processing. In the conventional approach to RFID tracking in mail processing, mail is sorted on an automated mail sorting machine such as an DBCS or MLOCR machine in use by the U.S. Postal Service. Such mail is swept from pockets of the sorter into trays by postal employees. Each tray has an RFID tag. In practice, this approach is problematic. After first processing, the manifest of mail sorted to a specific pocket is broken, i.e, sweeping loses definite association between mail and tray, so it cannot be known which of several successive trays a specific mail piece was placed in. Operator correlation of tagged tray and the letters it contains is unreliable and highly labor intense.
In another known approach, each mail piece is tagged with its own RFID tag, but this requires too many tags to be cost effective, and when tags are too close together they become difficult to read, hence such a system is unreliable.
Placement of RFID tags on less than all mail pieces in order to identify them has been proposed. See, for example, Sadatoshi et al. U.S. Patent Pub. 20050077353, which allows multiple mail pieces in a tray to be read by RFID. Most RFID readers presently available specify 4 inches between tags because the tag in front relative to the reader shades the one behind it. The system of Sadatoshi et al. solves that problem, but it only works if the tray is moved parallel and in close proximity to the reader antenna with mail perpendicular to the plane of movement. This could be made to work in a tray management system where the trays are moved down conveyors, but would not be practical for a cart of mail in trays.
A better approach is described in commonly assigned Redford U.S. Ser. No. 11/840,749, filed Aug. 17, 2007, the contents of which are incorporated by reference herein. In that application, a process of tracking mail during postal handling includes an initial step of sorting an incoming stream of mail on an automated sorting machine to a series of pockets based on a sort scheme. During sorting, RFID-tagged, machine-sortable markers are introduced into the incoming mail stream at intervals and the RFID-tagged markers are sorted with the mail into pockets of the sorter. Mail and markers are swept from the pockets into trays, and the markers are introduced such that at least one marker is swept to each of a set of trays containing the sorted mail. The trays containing the mail and markers are then transported away from the automated sorting machine. During a postal operation subsequent to the initial sorting, one or more of the RFID-tagged markers are scanned to identify mail from the initial sorting. As described, this method preferably utilizes RFID gateways through which carts carrying tagged mail trays must pass in order to move from one location within the postal facility to another. However these gateways require considerable cost to deploy, and thus it is a goal of the present invention to reduce the number of gateways needed for an RFID system such as the Redford '749 system. In addition, a gate-based system cannot identify where a specific tray is within an area that is between two RFID gates. In other words, the system can tell where a tray isn't, but not where it is, except at the moment it is passing through a gate. The present invention seeks to improve on these results.
A vision system was proposed for use in a parcel handling facility for the purpose of projecting handling instructions on or near a parcel on a conveyor. See Ramsager U.S. Pat. No. 7,090,134 describes a system for projecting a handling instruction onto a moving item or parcel. See also commonly assigned U.S. Ser. No. 12/266,779 filed Nov. 7 2008, the contents of which are incorporated by reference herein.